For several decades, linguists have described speech sounds using a “distinctive feature” representation, identifying a set of physiological actions or states which serve to distinguish speech sounds from one another. Phonemes are viewed as a shorthand notation for a set of features which describe the operations of the articulators required to produce the distinctive aspects of a speech sound. For example, the phonemes “p” and “b” are produced in ways which differ only in the state of the vocal folds; “p” is produced without vibration (unvoiced) while “b” requires vibration of the vocal folds (voiced). In the distinctive feature representation, only the feature “voice” differs for these two sounds.
An evolving need has been recognized in connection with representing the speech waveform in terms of the same set of distinctive linguistic features as are used to distinguish phonemes.